What are distributaries in the context of a delta?

Distributaries in the context of a delta refer specifically to channels that spread out across the delta region. When a river approaches its mouth and enters a delta, it begins to slow down and deposit the sediment it has been carrying due to the reduction in water velocity. This sediment deposition causes the river to split into smaller channels, known as distributaries, which fan out across the delta. These distributaries carry water and sediment away from the main river channel, allowing the delta to expand outward. They play a crucial role in the distribution of sediment, nutrients, and freshwater to the deltaic ecosystem, supporting a variety of wildlife and plant life.

The other options do not accurately describe distributaries. Large rivers that rejoin the main channel represent a different river dynamics process and do not reflect the branching nature of distributaries. Narrow channels on steep slopes tend to be associated with upper river systems rather than delta environments. Main channels carrying the most sediment do represent key elements of river systems, but they refer specifically to the primary flow of the river before it splits into distributaries. Thus, the definition of distributaries as channels that spread out across a delta accurately captures their function and significance in river delta morphology.